a round switch on a machine such as a radio that you use to turn it on and off, etc. （用以开关电视机等的）旋钮 
the volume control knob 音量控制旋钮 I've tried fiddling with the knobs, but nothing seems to happen. 我试着拨弄那些旋钮，但似乎什么作用也没有。
Oxford Collocations Dictionaryadjective- door
- control
- volume
- …
- adjust
- fiddle with
- touch
- …
- knob on
a round handle on a door or a drawer （门或抽屉的）球形把手 I tried the knob, and this time the door opened. 我试着旋动球形把手，这次门开了。 She turned the heavy brass door knob. 她转动门上沉重的黄铜球形把手。
Oxford Collocations Dictionaryadjective- door
- control
- volume
- …
- adjust
- fiddle with
- touch
- …
- knob on
a round shape like a ball on the surface or end of something 疙瘩；节 He carried a long cane, tipped with an iron knob. 他拿着一根长手杖，顶端有一个铁把手。 The bird's bill is orange with a black knob at its base. 这只鸟的喙是橙色的，底部有一个黑色的旋钮。
- (especially British English)
a small piece of something such as butter 小块（黄油等） - (British English, taboo, slang)
a penis 阴茎 More Like This Silent lettersSilent letters
Word Originlate Middle English: from Middle Low German knobbe ‘knot, knob, bud’.